The research proposed will study the mechanisms regulating transcription of the genes required for metabolism of L-arabinose in E. coli. Four objectives are planned. The first will be to learn the nucleotides of the regulatory region DNA that are required for normal control of the arabinose operon. Base changes that abolish activity will be learned by seqencing regulatory mutants. Also, modifications of the Maxam-Gilbert DNA sequencing method will be used to determine those bases that are protected from methylation by the presence of the regulatory complexes and to determine those nucleotides, which if modified, prevent the formation of the complexes. Additional araC protein responsive promoters, from E. coli, and other bacteria, will be isolated and sequenced. The second objective will be direct physical studies on the mechanism of regulation. Association rates of the proteins from wild-type and mutant cells will be measured by in vitro transcription and high resolution electron microscopy. Microscopy with bound antibodies will be used to determine which proteins remain in the regulatory complexes after they have formed on the DNA and approximately where within the complexes the proteins or subunits lie. The next objective will be to isolate and map many mutations in araC protein which inactivate each of its three functions. The final objective will be to predict the tertiary structure of araC protein from its amino acid sequence and to examine this for information on its mechanism of action.